1. Field of the Invention
The invention relates to a process for the catalytic ammoxidation of alkanes and olefins, more specifically C3 to C5 paraffins or olefins, such as propane or isobutane and propylene or isobutylene, to the corresponding α,β-unsaturated mononitriles, e.g., acrylonitrile and methacrylonitrile.
2. Description of the Prior Art
U.S. Pat. No. 6,710,207 discloses a method for producing an unsaturated carboxylic acid or an unsaturated nitrile, such as acrylic acid or acrylonitrile, by vapor phase catalytic oxidation of mixtures of alkenes and alkanes in the presence of a mixed metal oxide catalyst. Carbon dioxide is disclosed as an impurity in the feed, as a diluting gas for adjusting the space velocity and the oxygen partial pressure and as a by-product of the reaction.
U.S. Pat. No. 3,535,366 discloses a process for the production of terephthalonitrile by including an inert heat carrier gas, such as methane, ethane or carbon dioxide, which has a heat capacity higher than that of nitrogen to reduce hot spot temperature which results in improved selectivity. The heat carrier gas is present from 5 to 80%, preferably 5 to 40%, by volume.
U.S. Pat. No. 6,080,882 discloses a process for producing acrylonitrile or methacrylonitrile from propane or isobutane by ammoxidation in which the temperature is elevated to the ammoxidation reaction temperature while a molecular oxygen-containing gas and a combustible gas are supplied to the reaction zone. The molecular oxygen-containing gas may be diluted with an inert gas, such as nitrogen, argon, steam or carbon dioxide.
U.S. Pat. No. 5,015,576 discloses a process for production of nitrites from hydrocarbons by reaction with an oxygen-containing gas, such as oxygen, air or a gas enriched in oxygen, and ammonia in the presence of a catalyst and a gaseous flame suppressor. The gaseous flame suppressor contains a substantially unreactive hydrocarbon having from 1 to 5 carbon atoms, carbon dioxide and, where air or enriched air is utilized as the oxygen-containing gas in the feed to the ammoxidation reactor, nitrogen.
Prior art discloses the addition of certain compounds to the feed to improve catalyst performance. U.S. Pat. No. 3,746,737 discloses a process for the production of acrylonitrile or methacrylonitrile by vapor phase reaction of a mixture of a hydrocarbon, such as propane or isobutane, ammonia and oxygen in the presence of a Mo—Ce catalyst and a halogen or a halide compound for improved conversion and selectivity.
U.S. Pat. No. 3,833,638 discloses preparation of acrylonitrile or methacrylonitrile from a mixture of propane or isobutane, ammonia and oxygen in the presence of a Mo—Ce catalyst optionally in the presence of a halogen or a halide compounds or sulfur or hydrogen sulfide for improved conversion and selectivity.
U.S. Pat. Nos. 4,000,178, 4,101,188 and 5,576,469 also disclose the addition of halide compounds as promoters in an ammoxidation reaction using antimony-containing catalysts. U.S. Pat. No. 3,696,267 also discloses sulfur in the ammoxidation of saturated hydrocarbons using an antimony-uranium catalyst to improve conversion and yield of unsaturated nitriles.
U.S. Pat. Nos. 5,332,855 and 5,334,743 disclose ammoxidation of alkanes, such as propane, from a reactive gas of saturated hydrocarbon, ammonia, oxygen and an inert diluent and/or steam.
While carbon dioxide had been disclosed as present in a process for the ammoxidation of an alkane to an unsaturated nitrile, carbon dioxide has not been disclosed as beneficial to the selectivity to the nitrile product.